Sandy and Global Warming
Quite a lot of people have been offering the destruction due to Sandy as evidence of the evil consequences of global warming. As best I can tell, this claim is supported by three arguments, two of which are wrong and one at least disputable.
The first argument is that Sandy was the worst storm to ever hit New York, as measured by the storm surge:
"On Monday, sea levels in New York City reached about 14 feet above the average low-tide mark; more than 9 feet above the average high; almost 3 feet above the last record, set in 1821."(Craig Childs, N.Y. Times Op-Ed)
That sounds impressive—if you ignore the fact that Sandy happened to hit at high tide. According to one discussion of the question I have seen—readers are welcome to correct it if mistaken—the 1821 hurricane hit at low tide. If we measure the strength of the storm by how much higher the sea level was than it would have been without it, we have to compare the earlier storm to the low tide level, Sandy to the high. By that measure, the 1821 storm was three feet worse than Sandy, not three feet better. So far as I know, nobody has yet tried to argue that global warming increases the probability that a storm will come to shore at high tide instead of low.
The second argument is that Sandy was so severe because global warming had raised sea levels. It is true that higher sea levels, all else being equal, result in more damage from flooding. But, checking Wikipedia, which shows sea level back to 1870, the increase since then has been only about eight inches, so it is hard to see how the effect could be very large.
The third argument, which might be right, is the claim that increased global temperatures result in more frequent or more violent storms. I looked into the question a few years ago, when the IPCC's Atlantic hurricane expert resigned in protest against the assertion, made by the person who was going to be coordinating that part of the next IPCC report, that hurricanes had become worse due to warming; the question was discussed at some length in a comment thread here. My conclusion was that the linkage was, at that point, speculative—it might be true, but the evidence was not sufficient to tell. I have not followed the argument since, beyond noting that some supporters of the claim seem to think it has been confirmed and some critics that it has not.